President Obama was in town to speak Tuesday morning at the United Nations, and Mitt Romney made a quick stop before heading out on a campaign bus tour of Ohio. But both candidates acknowledged by their presence that the former president’s annual confab on global development, timed to coincide with that other Manhattan gathering of world leaders (the UN General Assembly), is now a must-do for presidential aspirants.

Former Massachusetts Governor Romney – whose speech was almost simultaneous with Mr. Obama's UN address – offered a blueprint for a revamped foreign aid program. When his turn came, Obama focused on the scourge of human trafficking and what to do about it. In both cases, the appearances were about projecting gravitas and vision in the realm of foreign policy.

Romney, reflecting his business roots, made the case for foreign aid that focuses on the private sector and builds entrepreneurship. In his speech a few hours later, Obama said it is time to call the scourge of human trafficking what it really is: “modern slavery.”

In Romney’s critique of US foreign aid, the former CEO said Americans are generous and want to help the world, but have come to have little faith in foreign assistance. One reason the current model is not working, he said, is that it is designed for a world that no longer exists.

“Too often our passion for charity as a people is tempered by our sense that our aid is not always effective,” Romney said. “Perhaps some of the disappointments are due to our failure to recognize just how much the developing world has changed.”

Romney said that a much larger share of developing countries today are growing democracies with better-educated people and entrepreneurial communities. And he said that the most effective thing the US can do is to tap into this change and foster the same spirit that drives America’s prosperity.

“The aim of a much larger share of our aid must be the promotion of work and the fostering of free enterprise,” he said. “Nothing we can do as a nation will change lives and nations more effectively and permanently than sharing the insight that lies at the foundation of America’s own economy – and that is that free people pursuing happiness in their own ways build a strong and prosperous nation.”

By proposing to predicate US foreign aid on a country’s openness to US private investment and trade, Romney is touting an idea that is attractive to many Americans – and one that some past administrations have advocated. But development experts say it’s also a concept that runs into the reality of poor countries – Haiti and Afghanistan come to mind – that have little of the infrastructure required for taking advantage of private-sector investment.

Romney said the world also needs a re-do of the existing World Trade Organization in favor of one based on “the rules of free and fair trade.”

Obama, who has lost some of his international luster but nevertheless remains popular at the UN, arrived at the Clinton confab after a well-received UN speech focusing on Iran’s nuclear challenge and recent anti-American violence in some Muslim countries.

The US estimates that human trafficking affects more than 25 million people worldwide – including in the US.

"The ugly truth is that this goes on right here," he said. "It's the migrant worker unable to pay off the debt to his trafficker.... The teenage girl – beaten, forced to walk the streets. This should not be happening in America."

Anti-trafficking advocates say the fact the president would dedicate an entire speech to combating “modern slavery” is a hopeful signal that the issue – long swept under the rug even as it has burgeoned in a globalizing world – is garnering needed attention.

Obama pledged to make the US a “zero tolerance zone” for human trafficking, and said more government agencies and social partners, like schools, would be enlisted in the fight. Products made with slave labor will be off limits to government procurement, he said, while services for victims of trafficking will be beefed up.

Obama gave his speech and then left New York, skipping the round of bilateral meetings with world leaders that are normally part of the president’s September foray to the UN.

Some Republican critics blasted the president for appearing to put politics above America’s good standing with the world, but a number of world leaders said they understood why Obama cut short his time at the UN.

Mr. Hollande refused to say whom he preferred to see win the US election – “You can imagine what difficulty it would cause either candidate to be supported by a French Socialist!” – but he gave what may have been a hint. He said he wasn’t worried about not meeting Obama in New York, because he imagined there would be plenty of time for that after November.